Embodiments presented in this disclosure generally relate to computer networking and, more particularly, to techniques for providing a backup Dynamic Host Configuration Protocol (DHCP) server at a DHCP relay agent.
Internet Protocol (IP) addresses are used to designate the destination of IP communications. An IP address serves a purpose for network communications similar to a street address for postal mail. In order for a device (or node) connected to an IP network to communicate over the network with another node through an Internet Protocol, each node must have an IP address and each node must reference the IP address of the other node. Further, each node must be configured such that it is capable of determining a route to each other node with which it wishes to communicate. The IP address configuration information can be used to determine routes to other nodes for the purposes of communication form an IP Configuration for a node.
There are several methods to provide a node on a network with an IP Configuration. A node new to the network or which has been set to a factory default state may have a well known default IP configuration. For example, such a node could come preconfigured to use an address on a non-routable network. Alternatively, the IP network may utilize a DHCP server. The DHCP server may have available a pool of IP addresses and may assign an address from the pool to the node for a session on the IP network. In this case, a DHCP Client on the node must be configured to accept an IP address from a DHCP server. As another alternative, some combination of DHCP and default configuration may be used to assign a node an IP Configuration.
Generally, DHCP gives network administrators a method to facilitate automatic distribution of addresses and to maintain the network configuration in a central location. More specifically, DHCP is an application-layer protocol that allows a client machine on a network to exchange packets between a software daemon on the client (i.e., a DHCP client) with another on a DHCP server (i.e., a DHCP server application) to get an IP address. The DHCP server may lease the IP address to clients for some period of time, after which the lease of the IP address will expire. In such a scenario, the DHCP clients may have the option of renewing the lease of the IP address for an additional period of time. Additionally, such a period of time may be an infinite timeframe, such that the assigned IP address for the client remains the same without requiring renewal.